In the present article, the hydrogen evolution reaction in the mixed solution of H2O and D2O has been investigated on Pt and Ag electrodes via the electrochemical mass (EC-mass) spectroscopy. In addition to the metal species dependence, we have confirmed the morphological effect of the electrode surface on the isotopic effect. By the establishment of the EC-mass system, we have successfully discussed about the formation of the active sites which accelerated the hydrogen generation at the electrochemically roughened surface of Ag. The present results prove the importance of the in-situ mass spectroscopic measurement for the investigation to achieve the arbitrary control of the isotopic hydrogen evolution reactions. (C) 2019 Published by Elsevier Ltd.